1. Field of the Invention
The present invention relates generally to a method and apparatus for preventing the formation of snowmen within a clinker cooler. The invention relates more specifically to a method and apparatus which allow the monitoring and selective application of short duration blasts of high-pressure, high-velocity air through openings in the stepped supporting surface of a clinker cooler, jostling the clinker and thereby disrupting the accumulation of fines which grow to form snowmen, and dislodging any such accumulations in the clinker bed.
2. Description of Related Art
In the production of cement, raw materials are combusted to produce cement clinker, typically in a rotary kiln according to known methods. U.S. Pat. No. 5,437,721, to Kupper. et al., for example, describes one method of producing cement clinker from fine-grained cement raw materials.
Kiln temperatures of 1400.degree. C. and above are common in the production of cement clinker. The temperature of the clinker as it is discharged from the kiln is typically approximately 1350.degree. C. As the clinker exits the kiln, it must be cooled rapidly. Most commonly, the hot clinker is discharged from the kiln onto a grate constructed to facilitate the introduction of cooling air to cool the clinker. The clinker is exposed to cooling air while on the cooler inlet grate, and is then typically discharged to a conveyor which transports the clinker to a grinder or milling device.
A variety of cooling grates for cooling cement clinker have been developed and are known in the art. For example, U.S. Pat. No. 2,434,845 to Gaffney shows a clinker cooling chamber including a stepped grating onto which the hot clinker is discharged from the kiln. As the clinker moves downwardly, by gravity, along the grate, cooling air is introduced into the clinker pile through openings in the stepped surface.
Similarly, U.S. Pat. No. 4,732,561 to Eiring, et al. shows a cooling apparatus wherein hot material such as clinker, discharged from a kiln, is conveyed by gravity over a step-like series of air-permeable carrier elements. Cooling air is introduced to the material through the carrier elements, and may be delivered in pulses to individual carrier elements or groups of carrier elements.
The clinker typically discharged from a kiln is generally spherical and approximately one to three inches in diameter. Along with the clinker, "fines" are discharged from the kiln into the clinker cooler. These fines comprise smaller particulate matter and can cause a number of undesirable effects within the clinker cooler. For example, the fines can cling to the surfaces of adjoining pieces of clinker in the cooler and cause the clinker to clump together. This is referred to as agglomeration or caking. Also occasionally discharged from the kiln are large lumps of coating which have broken loose from the interior surface of the kiln. These large lumps interfere with effective heat transfer within the cooler and disrupt clinker flow through the cooler.
U.S. Pat. No. 4,870,913 to Schneider seeks to prevent caking in the clinker cooler by providing a grate cooler comprising stepped layers of grate plates, the forward facing surfaces of the grate plates having nozzle-shaped cooling air openings oriented to inhibit caking between the grate plates. Because the air supplied to its nozzle openings is drawn from the cooling air supply, Schneider is intended to prevent caking of clinker in localized areas. Schneider's air flow is insufficient to jar or shock the clinker itself, and is unable to dislodge fines which have already adhered to the clinker.
A more severe problem than that of caking of the clinker is the formation of "snowmen" in the clinker cooler. Snowmen are formed when fines fall from the kiln above, onto the top surfaces of large lumps of kiln coating on top of the clinker bed within the cooler. Snowmen also sometimes form on the top surfaces of the clinker, especially when the clinker cakes together. As layer after layer of the fines fuse onto the lump of kiln coating, snowmen "grow" upwardly into stalagmite-like structures. In effect, the lumps of kiln coating act as "seeds" for the formation of snowmen. Left unchecked, these snowmen may eventually grow to reach the mouth of the kiln, thereby blocking the discharge of clinker from the kiln.
To date, several attempts have been made to prevent the formation of snowmen. For example, U.S. Pat. No. 5,330,350 to Tegtmeier, et al. discloses a reciprocating grate cooler having a hydraulic mechanism for driving the cooler inlet grate in a reciprocating manner. It is also known to provide a rotating ram and thrust bar, such as that shown by U.S. Pat. No. 4,732,561 to Eiring, et al., which is mechanically driven to break-up any deposits or encrustations on the clinker.
These and other known methods and devices have been found less than entirely satisfactory to remove lumps of kiln coating from the cooler inlet, or to prevent the formation of snowmen. This is, in part, because such devices suffer the disadvantage that, by their nature, they inherently incorporate moving parts. Due to the weight of the clinker and its abrasive nature, these moving parts are highly susceptible to wear and breakage, especially at the high temperatures commonly encountered within the cooler. Moreover, the presence of fines from the kiln within the cooler environment can lead to the clogging and jamming of moving parts. Also, because the large lumps of kiln coating tend to float or ride on the surface of the clinker bed, reciprocating scrapers or thrust bars, which operate entirely beneath the surface of the clinker bed, are incapable of removing them from the cooler inlet.
It has also been proposed to direct pulses of high pressure air onto the clinker from openings in the cooler walls or in refractory walls within the cooler. In some instances, this has proven successful in shearing off the tops of snowmen in the immediate vicinity of the air openings. The lower portions of the snowmen, however, remain in place on the clinker bed and serve as seeds for the formation of new snowmen. Furthermore, because the air openings are located generally at the outer periphery of the cooler, the air pulses are unable to affect snowmen or other accumulations nearer to the center of the cooler. Also, except for air pulses from openings in the headwall at the back of the cooler, it is not possible for such an apparatus to direct air pulses in the direction of clinker flow. This limits the ability of such devices to move large lumps of kiln coating any significant distance from the headwall. This arrangement also suffers the disadvantage that, once the air openings are provided in the cooler walls, their position is fixed. As the depth of the clinker bed varies, the location of these openings may render them ineffective.
Thus, it can be seen that there exists a need for a method of preventing the formation of snowmen by removing lumps of kiln coating from the cooler inlet. A need further exists for a method of dislodging snowmen, once formed, during cooling. Likewise, a need exists for the provision of an apparatus capable of carrying out these methods, without the need for moving parts, and which is not affected by variations in the depth of the clinker bed.
It is to the provision of such a method and apparatus that the present invention is primarily directed.